Uncontrolled growth of microorganisms can have serious consequences such as degradation or spoilage of products, contamination of products, and interference with a wide range of important industrial processes. Growth of microorganisms on surfaces exposed to water (e.g., recirculation systems, heat exchangers, once-through heating and cooling systems, pulp and paper process systems, etc.) can be especially problematic, because biofilms can be formed by the indigenous microbial species. Depending on the environment, biofilms may develop into thick gelatinous-like masses and are referred to as slime. Slime producing microorganisms include bacteria, airborne microorganisms, sulfate reducing bacteria, filamentous bacteria, spore forming bacteria, fungi and algae.
Slime formation becomes especially problematic in industrial settings, because the presence of slime can interfere with a range of processes, systems, and production. As an example, slime deposits deteriorate cooling towers made of wood and promote corrosion when deposited on the metal surfaces of cooling water systems. Furthermore, slime deposits tend to plug or foul pipes, valves and flowmeters and reduce heat exchange or cooling efficiency on heat exchange surfaces.
Paper production is adversely affected by slime formulation. Pulp and paper mill systems operate under conditions which encourage the growth of microorganisms and often result in fouling problems. Moreover, microorganisms can form large slime deposits which can become dislodged from system surfaces and become incorporated into the paper, which results in increased breaks and tears in the sheet. Furthermore, slime can cause unsightly blemishes or holes in the final product, which result in a lower quality product or the product being rejected. This necessitates shutting down the paper making process to clean the equipment, which results in the loss of production time.
Slime may also be objectionable from the standpoint of cleanliness and sanitation in breweries, wineries, dairies and other industrial food and beverage process water systems. Moreover, sulfate reducing bacteria are often problematic in waters used for the secondary recovery of petroleum or for oil drilling in general. Sulfate reducing bacteria can form slime deposits. However, the real problem with sulfate reducing bacteria is that they become incorporated into well-established biofilms and generate by-products that have highly offensive odors, are toxic, and can cause corrosion of metal surfaces by accelerating galvanic action. For example, these microorganisms reduce sulfates present in the injection water to generate hydrogen sulfide. Hydrogen sulfide has a highly offensive odor (i.e., rotten egg smell), is corrosive and reacts with metal surfaces to form insoluble iron sulfide corrosion products.
The proliferation of bacteriological contamination in lubricants and cutting fluids is a common problem due to the elevated temperatures and unsanitary conditions found in many metal working plants. It is often necessary to discard these fluids due to microbiological contamination.
In order to control the foregoing problems in various industrial processes, numerous antimicrobial agents (i.e., biocides) have been employed to eliminate, to inhibit or to reduce microbial growth. These biocides are used alone or in combination to prevent or control the problems caused by growth of microorganisms.
Biocides are classified as oxidizing or non-oxidizing, depending on their chemical composition and mode of action. Whether an oxidizing or non-oxidizing biocide is used alone or in combination is dependent upon the problematic microorganism(s), the nature of the medium to which the biocide is added, as well as specific requirements of the industry, including safety and regulatory considerations.
Oxidizing biocides have been widely used in the industry for decades, especially in pulp and paper production where strong oxidizers have been used to control microbial populations. An important aspect of using an oxidizing biocide as a microbiological control program is to apply quantities sufficient to maintain a free oxidizer residual in the process. This can be problematic in process waters that contain high concentrations of dissolved and particulate inorganic and organic materials. Such process waters exhibit a high and variable “demand” on the oxidizer (i.e., the oxidizer can react with the inorganic and organic materials and be rendered ineffective as a biocide). The type and amount of inorganic and organic materials within the process streams, therefore, will determine the demand. For example, oxidizing biocides are consumed by inorganic species such as ferrous iron, reduced manganese, sulfides, sulfites, etc. as well as organic compounds such cellulosic fibers and additives. Thus, the demand of a system will increase with increasingly higher concentrations of inorganic and organic materials along with adverse physical conditions such as temperature and pH within those systems.
In order to overcome the demand of a system and achieve a free oxidizer residual, sufficient quantities of the oxidizer must be added. Although it is technically simple to feed quantities of oxidizing biocides to exceed the demand, this is often not practical. Not only do treatment costs increase with higher addition rates, but many adverse side effects in the industrial system can be manifested. The adverse effects will be system dependent.
In paper making systems, strong oxidizers, such as sodium hypochlorite, are often used for controlling the growth of microorganisms in order to prevent adverse effects on the papermaking process. Frequently, however, strong oxidizers such as sodium hypochlorite can cause more problems on the machine than they remedy. In papermaking systems, the side effects of strong oxidizers can be, among others, increased corrosion rates, increased consumption of dyes and other costly wet end chemicals (e.g., brighteners, dry and wet strength additives, and sizing agents), and reduced felt life.
Ammonium bromide activated with sodium hypochlorite has been shown to be an effective biocide for industrial applications (U.S. Pat. No. 5,976,386). This biocide is especially effective in pulp and paper process systems. Specifically, ammonium bromide effectively reduces the total microbial community within a system (i.e., sessile as well as planktonic bacteria) and helps in the removal of slime deposits from surfaces. Moreover, it does this without interfering with other pulp and paper process and functional additives (e.g., wet and dry strength additives, size agents, dyes, etc), unlike other common oxidizer programs. Considering the benefits of an ammonium bromide-based biocide program, it is likely that the active chemical species has a mode of action that differs from hypochlorite or other strong oxidizers. Therefore, it was surprising to find a significant synergy between ammonium bromide activated with sodium hypochlorite and other biocides.
U.S. Pat. No. 6,222,071 disclosed the manufacture of high grade chloramine wherein sodium hypochlorite solution is reacted with a combined mixture of ammonia and ammonium salts at low temperatures.